1/4" Quick Connect Clip for under sink filters.

thingiverse

First design works like a charm. Easy little clip holds under sink water filter fittings securely in place. Not necessary, but it's there and makes installation safer overall. One thing I'd change if redoing it is making the handle bigger for easier removal. It needs to be just big enough to get your fingernail in, but since you won't need to take it out often, it's not a huge deal.